212 PRESP^NT PROBLEMS OF INORGANIC CHEMISTRY. 



liowcvfi'. llial at low t(Mii|)('ratiires c()m])()un(ls could he formod in 

 wliidi one of the eleiueiits would possess a i2;reater valency than that 

 usually ascribed to it : and also that double compounds of greater 

 complexity would prove stable. Valency, indeed, appears to be in 

 many cases a function of temperature; exothermic compounds, as 

 is Avell knoAvn, are less stable the higher the temperature. The sud- 

 den cooling of com])ounds produced at a high temperature may pos- 

 sibly result in forms being preserved which are' unstable at ordinary 

 temperatures. Ex^Deriments have been made in the hope of obtaining 

 compounds of argon and helium l^y exposing various elements to the 

 influence of sparks from a powerful induction coil, keeping the walls 

 of the containing vessel at the temperature of liquid air, in the hope 

 that any enclothermic compound which might be formed would be 

 rapidly cooled and would survive the interval of temperature at 

 which decomposition would take place naturally; But these experi- 

 ments have, so far yielded only negative results. There is some indi- 

 cation, however, that such compounds are stable at 1,500°. It might 

 be hoped that a study of the behavior of the nonvalent elements 

 Avould' have led to some conception of the nature of valency, but so 

 far no results bearing on the question have transpired. The condi- 

 tion of helium in the minerals from Avhich it is obtainable by heat is 

 not explained, and experiments in this direction have not furnished 

 any positive information. It is always doubtful whether it is advis- 

 able to publish the results of negative experiments, for it is always 

 possible that some more skilled or more fortunate investigator may 

 succeed where one has failed. But it ma}^ be chronicled that attempts 

 to cause combination between the inactive gases and lithium, potas- 

 sium, rubidium, and ca'sium have yielded no positive results, nor 

 do they appear to react with fluorine. Yet conditions of experiment 

 play a leading part in causing combinations, as has been well shown 

 by Moissan with the hydrides of the alkali metals, and b}^ Guntz, 

 with those of the metals of the alkaline earths. The proof that 

 sodium hydride possesses the formula NaH, instead of the formerly 

 accepted one, removes one difficulty in the problem of valency, and 

 SrH^, falls into its natural position among hydrides. 



A fertile field of inorganic research lies in the investigation of 

 structure. "While the structure of organic compounds has been eluci- 

 dated almost completely, that of inorganic compounds is practically 

 undeveloped. Yet efforts have been made in this direction which 

 appear to point a way. The nature of the silicates has been the sub- 

 ject of research for many j^ears by F. AV. Clarke, and the way has 

 been opened. Much may be done by treating silicates with appropri- 

 ate solvents, acid or alkaline, which differentiate^ between uncombined 

 and combined silica, and which in some cases, by replacement of one 

 metal by another, gives a clue to constitution. The complexity of the 



